Water-resistant consumable cartridge case

ABSTRACT

Novel water-resistant consumable cartridge cases are made from fibrous organic derivatives of cellulose, e.g., cellulose stearate acetate mixed ester, which absorb less than about 6 percent by weight of moisture. The cartridge cases are produced by compression molding a plastic mixture of the particulate fibrous cellulose derivative and a polymerizable composition capable of forming a rigid, cross-linked water insoluble polyurethane or other resin, and thereafter forming the resin.

ilttitte tates Patent [1 1 Bobinslri et a1.

[ NOV.6,1973

1 WATER-RESISTANT CONSUMABLE CARTRIDGE CASE [75] Inventors: JackBobinski, Mt. Lakes; Jean P.

Picard, Morristown, both of NJ.

[73] Assignee: The United States of America as represented by theSecretary of the Army, Washington, DC.

[22] Filed: Jan. 26, 1971 [21] Appl. No.: 109,952

[52] 11.8. C1 161/162, 102/38, 102/43 A, 102/43 R,102/D1G. 1,161/168,161/184 [51] Int. Cl. F42b 9/14, F42b 39/02, F42b 5/30 [58] Field ofSearch 161/162, 168, 184; 260/13; 102/38, 43 P, 43 R, DIG. l

[56] References Cited UNITED STATES PATENTS 3,676,233 7/1972 Netzer etal. 102/D1G. 1

3,670,649 6/1972 Hartlein et a1 102/43 R 3,139,355 6/1964 DeFries etal... 102/43 R 3,513,776 5/1970 Driscoll 102/43 R 3,280,746 10/1966Brown 102/43 P 2,137,350 1l/l938 Roberts 102/43 P 1,880,808 10/1932Clarke et a1. 260/225 3,257,948 6/1966 Axelrod et al..... l02/D1G. 13,542,740 11/1970 Pumpelly et al. 260/13 2,879,235 3/1959 Condo 260/132,865,870 12/1958 Pinder 260/13 601,902 4/1898 Oliver 102/D1G. 13,397,637 8/1968 Bobinski et a1. 102/38 3,504,630 4/1970 Picard 102/43 RPrimary ExaminerWilliam J. Van Balen Att0rneyHarry M. Saragovitz, EdwardJ. Kelly, Herbert Berl and A. Victor Erkkila [57] ABSTRACT 7 Claims, NoDrawings Bowman 260/13 WATER-RESHSTANT CONSUMABLE CARTRIDGE CASE Thepresent invention relates to novel water-resistant consumable cartridgecasing material and to methods for making same.

Non-metallic, consumable cartridge cases prepared from cellulose aregenerally unsatisfactory due to the tendency of the cellulose to absorbmoisture from the atmosphere, causing it to soften and swell and renderthe case weak and unfit for use. To overcome this difficulty varioustreatments designed to waterproof the case have been proposed, such ascoating the case with a water-insoluble wax or lacquer, or impregnatingthe porous cellulosic casing material with a solution of awater-insoluble resin followed by heating to evaporate the solvent andcure the resin. Another method is to place the cellulosic cartridge casecontaining propellant charge in a sealed bag made of film of hydrophobicorganic resin such as polyethylene. None of the prior art methods orcompositions have proved entirely satis factory.

An object of this invention is to provide a novel consumable cartridgecase material of high water resistance combined with good strength.

Another object of the invention is to provide a process for producingsuch novel consumable cartridge case material, which is simple, safe andeliminates the need for special water-proofing treatments.

Other objects of the invention will appear or be obvious from thedescription of the invention set forth below.

Our investigations have revealed that certain organic derivatives ofcellulose of fibrous nature possess very low moisture absorptionproperties. Our studies have further shown that such fibrous organicderivatives of cellulose, by virtue of their extremely lowhygroscopicpractically hydrophobicproperties and their fibrous, porousnature, are uniquely suited for producing highly water-resistantcartridge cases, which possess sufficient porosity to permit completecombustion thereof when fired with a suitable propellant.

Thus, in accordance with this invention such novel consumable cartridgecases can be obtained by compressing a homogeneous plastic mixtureconsisting essentially of l particles of a fibrous organic derivative ofcellulose of low hygoscopicity, i. e., which absorb less than about 6percent by weight of water at equilibrium in 90 percent relativehumidity at 25 C, and

2. a polymerizable composition capable of forming a rigid, cross-linked,water-insoluble resin, into a suitable shape and thereafter curing theresin. The resulting product contains the particles of fibrous organiccellulose derivative embedded in and/or bonded together by thewater-insoluble organic resin into a rigid, porous structure possessingexcellent resistance to water combined with good strength anddimensional stability.

A suitable method for making the novel cartridge cases comprises firstmechanically mixing the fibrous cellulose derivative with thepolymerizable resin composition until a homogeneous plastic mixture isobtained, then compressing the mixture into a suitable shape, e.g., tubeor case, by extrusion molding or compression in a mold, and finallyheating the product to cure the resin. When a liquid polymerizable resincomposition is employed, it can be mixed directly with the organiccellulose derivative, which is usually in the form of a powder orparticles less than about onesixteenth inch in their. longest dimension.If the polymerizable resin composition is a solid, it can first bedissolved in a solvent which does not dissolve the organic cellulosederivative, and the resulting solution then mixed with the particulatecellulose derivative to provide a plastic mixture suitable for molding.By judicious selection of molding conditions, proportion of resinemployed with the fibrous cellulosic derivative, degree of porosityproduced etc., a cartridge case can be ob tained which is completelyconsumable when charged and fired with a propellant.

Organic derivatives of cellulose which can be employed in this inventioninclude organic carboxylic acid esters of cellulose, particularlycellulose esters of hydrocarbon monocarboxylic acids containing at least6 carbon atoms, such as caproic-, lauric-, stearic-, oleicand linoleicacids. Such cellulose esters can be obtained by reacting cellulose, suchas cotton fiber or bleached sulfite wood pulp, or a cellulose derivativesuch as cellulose monoor diacetate, with a suitable carboxylic acid,such as stearic acid, alone or in mixture with another carboxylic acidsuch as acetic acid, in the presence of an organic solvent for thecarboxylic acid and a catalyst for the reaction e.g., trifluoraceticanhydride. The cellulose ester thus obtained can be precipitated bydiluting the reaction mixture with methanol. The precipitated productcan be purified by dissolving it in a water-miscible solvent such astetrahydrofuran and pouring the resulting solution into water, whereby afibrous product is obtained as a precipitate which can be separated byfiltration, washed with water and dried. The preparation of suchcellulose esters and mixed esters is illustrated in example 1 below andis further described in the prior art, e.g., U.S. Pat. No. 1,880,808.

The following illustrate additional cellulose esters which are suitablefor use in this invention: The degree of substitution (DS) is shown inparentheses.

l. cellulose acetate (2.45) oleate (0.19) stearate (0.22) waterabsorption 2.0 percent 2. cellulose acetate (2.4) stearate (0.2) waterabsorption 3.4 percent 3. cellulose crotonate (2.9) water absorption 5.4

percent 4. cellulose stearate (0.4) crotonate (0.1) water absorption 4.1percent 5. cellulose acetate (2.4) acid phthalate (0.1) water absorption3.6 percent All of the foregoing cellulose esters absorb less than 6percent by weight of moisture in percent relative humidity at 25 C(equilibrium condition). Fibrous organic derivatives of cellulose whichabsorb substantially more than about 6 percent by weight of moistureunder such conditions are generally unsatisfactory for use in thisinvention'as they produce cartridge cases, which on exposure to theatmosphere absorb unduly large amounts of moisture and cause the case toswell excessively, and may not be combustible.

For bonding the organic cellulose derivative particles according to thisinvention any polymerizable composition may be employed, which iscapable of producing a water-insoluble, rigid organic resin, such as forexample cross-linked polyurethane, epoxy and polyester res- Suitablerigid polyurethane resins can be obtained in known manner, for example,by reacting an organic polyisocyanate and an organic polyol in thepresence of a cross-linking agent, e.g., a compound containing three ormore functional groups, e.g., NCO, OH, and NH groups, (which may beprovided by the organic polyisocyanate, polyol or another organiccompound) to produce a rigid cross-linked resin. Illustrative organicpolyisocyanates are toluene- 2,4- diisocyanate, 4,4'- diphenylmethanediisocyanate, polymethylene polyphenylisocyanates obtained byphosgenating polyamines containing more than 2 primary amino groupsproduced by condensation of aniline with formaldehyde, and prepolymerscontaining two or more terminal isocyanate groups, e.g., the diandtriisocyanates obtained by reacting one mol of a diol or triol with twoand three mols of toluene diisocyanate resp. Illustrative polyolsinclude ethylene glycol, glycerol, 1,2,6- hexanetriol, pentaerythritoland polyether polyols obtained by reacting such polyols with ethyleneand1,2- propylene oxides, polyester polyols obtained by reacting apolycarboxylic acid e.g., adipic and succinic acids, with an organicpolyol e.g., ethylene glycol and polyethylene glycols, etc. A suitablecatalyst may be added to accelerate the reaction as is well known, e.g.,stannous octoate, triethylene diamine and phenyl mercuric acetate.

Suitable epoxy resins can be prepared, for example, by heating apolyglycidyl ether obtained by reaction of epichlorohydrin with apolyhydric phenol, e.g., 4,4- dihydroxydiphenyl methane and novolacresins, with a cross-linking agent, e.g., an organic polyamine e.g.,mphenylenediamine or a polycarboxylic acid or anhydride e.g., phthalic-,tetrahydrophthalic and dodecenyl succinic anhydride, in the presence ofa catalyst, e.g., dimethylbenzylamine. Polyester resins which can beemployed in this invention include those obtained in known manner byreacting an unsaturated polyester, e.g., polyethylene maleate orfumarate, with a suitable cross-linking agent, such as styrene.

The preferred resins for use in this invention are epoxy resins obtainedby reacting a polyglycidyl ether from epichlorohydrin and 2,2'-bis(4-hydroxyphenyl) propane with an organic polyamine, since they provideexcellent curing properties and produce cartridge cases of optimumphysical properties.

A degree of porosity ranging from about 30 percent to about 70 percentis usually satisfactory (percent porosity, as usually determined,represents the ratio of the bulk density to the intrinsic density of thecase). Generally, an amount of the water-insoluble resin binder fromabout 30 to about 70 percent, based on the com bined weight of the resinbinder and organic cellulose derivative, is satisfactory. Smallerproportions of the resin binder, e.g., as low as about percent byweight, can be employed, although the strength of the case generallydecreases as the proportion of resin binder is thus reduced.

The following examples illustrate the invention.

Example 1 A uniform mixture of the following materials was placed in amold:

1. 15 grams of fibrous cellulose acetate linoleate stearate, prepared asdescribed below and containing 2.4 acetate groups, 0.2 linoleate groupand 0.2 stearate group per anhydroglucose residue.

2. 15 grams of an epoxy resin of mol. wt. 380, obtained by reacting2,2-bis (4- hydroxyphenyl) propane with epichlorohydrin (a commercialproduct known as Epon Resin 828 marketed by Shell Chemical Co.)

3. 15 grams of a polyamide containing free amino groups obtained byreaction of ethylenediamine and linoleic acid dimer (a commercialproduct known as Versarnid 125 supplied by Stephenson Chemical Co. Inc.)

4. 25 ml. of methanol The mold comprised a vertical cylindrical tube ofl k in. ID. closed at its lower end, and a cylindrical piston of l /4in. OD. adapted to move downwardly in the tube in concentric alignment.The piston was then forced into the tube, thereby compressing themixture and causing it to rise into the annular space between the pistonand inner tube wall. The mold was then opened and the tubular case,about 5 in. long, 1 5% in. ID. and as in. wall thickness formed thereby,was removed and maintained first at room temperature for several hoursand thereafter at C for 2 hours to cure the epoxy resin.

The cartridge case thus obtained possessed the following properties:

moisture absorption (equilibrium conditions at combustibility completelycombustible, left no residue when fired with conventional propellant at16,000

PSI.

The cellulose acetate linoleate stearate employed in the example wasprepared as follows:

A mixture of grams of commercial cellulose acetate (degree ofsubstitution DS 2.45, i. e., 2.45 acetate groups per anhydroglucoseresidue) 80 grams of linoleic aci 80 grams of stearic acid 160 ml. oftrifluoroacetic anhydride 400 ml. of ethylene dichloride was heated to60 C with agitation for 1 1% hours, then allowed to cool to about roomtemperature and slowly stirred into 2,500 ml. of methanol. The resultingprecipitate was separated by filtration, washed with methanol and airdried. The product thus obtained was purified by dissolving it intetrahydrofuran, and pouring the resulting solution slowly into a largevolume of water to precipitate the product as a white fibrous material,which was isolated by filtration and dried.

Example 2 epoxy resin-polyamide content 47 to 57% by wt porosity 35 to70% tensile strength 940-980 psi elongation 3.5% approximately moistureabsorption (equilibrium conditions at relative humidity at 24C) 2.5%

combustibility left no residue when fired with a conventional propellantat 16,000 psi. Prolonged contact of the cases with water had anegligible effect on their rigidity and dimensional stability.

The cellulose stearate oleate employed above was obtained as follows:

A mixture of 20 g. Kraft pulp 20 g. stearic acid 20 g. oleic acid 40 ml.trifluoroacetic anhydride, and

400 ml. ethylene dichloride was heated to boiling and refluxed withagitation for 6 hours. The reaction mixture was then allowed to cool andfiltered, and the filter cake of fibrous mixed cellulose ester waspurified by washing with methylene chloride and dried.

Example 3 A. Preparation of the Organic Derivative of Cellulose Asolution of 80 grams of cellulose acetate hydrogen phthalate containing1.2 acetate and 0.8 phthalate groups per anhydroglucose residue(obtained by refluxing a mixture of cotton linters, acetic acid,phthalic acid, trifluoroacetic anhydride and tetrahydrofuran andthereafter pouring the reaction mixture into water to precipitate thecellulose acetate phthalate mixed ester) 64 grams of an isocyanateterminated polyester containing 6.5 percent by wt. free NCO group and ofm. p. 42-47 C., marketed as Multrathane F-242 by the Mobay Chemical Co.,and 0.4 gram stannous octoate in 1,800 ml. of tetrahydrofuran was heatedto boiling and refluxed under ordinary pressure for three hours. Thereaction mix ture was then cooled to room temperature and slowly pouredinto 4,000 ml. of water with agitation. The fibrous precipitate thusobtained was washed with water and then reduced to fibers of about H32in. length (average) in a Waring blender and dried. The dry cellulosederivative thus obtained absorbed 4.8 percent by weight of moisture at90 percent rel. humidity and 24 C. at equilibrium condition. (Itcontained free hydroxy groups but no free carboxyl groups by infra redanalysis) B. Preparation of the Non-hygroscopic, Consumable CartridgeCase 100 grams of the cellulose derivative obtained in part A above 100grams of Multrathane F-242 2.4 grams of l,4-butanediol 3.6 grams ofdiethyleneglycol 0.5 gram of stannous octoate 350 grams ofethylenedichloride were mechanically blended and the uniform mixturethus obtained was extrusion molded to form a sleeve, which was thenheated to about 120 C for about 6 hours to polymerize and cure thepolyurethane resin.

The product thus obtained possessed the following properties:

erosion apparatus at 16,000 psi. when fired with a conventionalpropellant From the foregoing it can be seen that the invention providesa number of valuable and unobvious advantages over the prior art. Thus,it utilizes essentially nonhygroscopic fibrous organic derivatives ofcellulose as a novel class of materials for manufacturing consumablecartridge cases. The novel use of such cellulose derivatives accordingto this invention avoids the hazards associated with the application ofelevated curing tem- 10 peratures and molding and extrusion pressures inthe manufacture of consumable cases from potentially explosivematerials, such as nitrocellulose previously employed. Also,nitrocellulose is undesirable for making consumable cartridge cases,since it gradually decomposes on exposure to air and light. Further, thenovel cartridge cases can be readily prepared simply by compressing amixture of such particulate cellulose derivative and polymerizable resincomposition into a desired shape and then forming the polymerized resin.The method is simple and safe. The novel consumable cartridge cases ofthis invention, unlike cases previously prepared with cellulose fibers,do not absorb water or swell and become unusable; and unlike casesprepared from nitrocellulose, they can be inserted into the chamber of acannon etc. hot from previous firings, without danger of prematureexplosion or fire. Also, by virtue of the fibrous, porous structure ofthe organic cellulose derivative, the novel cartridge cases preparedtherewith according to this invention can be provided with sufficientporosity to permit of their complete combustion under firing conditions.

We claim:

1. A consumable cartridge case of good water resistance and dimensionalstability, consisting essentially of particles of a fibrous celluloseester of a carboxylic acid, which absorb less than 6 percent by weightof water, bonded together into a porous structure with awater-insoluble, rigid, cross-linked organic resin selected from thegroup consisting of epoxy and polyurethane resins, said case having aporosity between about 30 percent and about percent and containing fromabout 30 percent to about 70 percent of said organic resin based on thecombined weight of said resin and said cellulose ester.

2. The case according to claim ll wherein the resin is an epoxy resinobtained by reacting a polyglycidyl ether, produced by reaction ofepichlorohydrin with 2,2-bis (4-hydroxyphenyl) propane, with a polyaminecross-linking agent.

3. The case according to claim 2 wherein the cellulose ester is selectedfrom the group consisting of cellulose acetate stearate, celluloseacetate stearate oleate, cellulose acetate phthalate, cellulose stearateoleate, cellulose acetate linoleate stearate and cellulose stearatecrotonate.

4. The case according to claim 2 wherein the polyamine cross-linkingagent is a polyamide containing free amino groups obtainable by reactingethylenediamine and linoleic acid dimer.

5. The case according to claim 2, which exhibits a water absorption notgreater than about 2.5 percent at percent relative humidity at 24 C.

6. The case according to claim 4, wherein the cellulose ester is acellulose stearate oleate mixed ester and the case possesses a contentof 47-57 percent of said epoxy-polyamide resin, a porosity of 35-70percent, a moisture absorption of not more than about 2.5 percent at 90percent relative humidity at 24 C, a tensile strength of 940-980 psi andan elongation of about 3.5 ylic acid comprises a hydrocarbonmonocarboxyiic percent. acid containing at least 6 carbon atoms.

7. The case according to claim 1, wherein the carbox-

2. The case according to claim 1 wherein the resin is an epoxy resinobtained by reacting a polyglycidyl ether, produced by reaction ofepichlorohydrin with 2,2-bis (4-hydroxyphenyl) propane, with a polyaminecross-linking agent.
 3. The case according to claim 2 wherein thecellulose ester is selected from the group consisting of celluloseacetate stearate, cellulose acetate stearate oleate, cellulose acetatephthalate, cellulose stearate oleate, cellulose acetate linoleatestearate and cellulose stearate crotonate.
 4. The case according toclaim 2 wherein the polyamine cross-linking agent is a polyamidecontaining free amino groups obtainable by reacting ethylenediamine andlinoleic acid dimer.
 5. The case according to claim 2, which exhibits awater absorption not greater than about 2.5 percent at 90 percentrelative humidity at 24* C.
 6. The case according to claim 4, whereinthe cellulose ester is a cellulose stearate oleate mixed ester and thecase possesses a content of 47-57 percent of said epoxy-polyamide resin,a porosity of 35-70 percent, a moisture absorption of not more thanabout 2.5 percent at 90 percent relative humidity at 24* C, a tensilestrength of 940-980 psi and an elongation of about 3.5 percent.
 7. Thecase according to claim 1, wherein the carboxylic acid comprises ahydrocarbon monocarboxylic acid containing at least 6 carbon atoms.